What causes elevated neutrophil (white blood cell) count?

Causes of Elevated Neutrophil Count

Bacterial infection is the most common cause of an elevated neutrophil count, warranting careful assessment even in the absence of fever. 1, 2

Infectious Causes

• Bacterial infections are the most common cause of neutrophilia, with a high likelihood ratio for bacterial infection when neutrophil count is elevated 1, 2
• An elevated total band neutrophil count (≥1500 cells/mm³) has the highest likelihood ratio (14.5) for detecting documented bacterial infection 1
• An increase in the percentage of neutrophils (>90%) has a likelihood ratio of 7.5 for bacterial infection 1
• A left shift (≥16% band neutrophils) has a likelihood ratio of 4.7 for bacterial infection, even with a normal total WBC count 1
• Specific bacterial infections commonly causing neutrophilia include respiratory tract infections, urinary tract infections, skin/soft tissue infections, and gastrointestinal infections 2
• Spontaneous bacterial peritonitis in patients with cirrhosis and ascites often presents with altered white blood cell count 1

Non-Infectious Causes

• Acute physiologic stressors can cause neutrophilia through several mechanisms 3:
  • Surgery and trauma trigger neutrophil release from bone marrow storage 3, 4
  • Exercise and emotional stress can cause rapid mobilization of the marginated neutrophil pool 3
  • Corticosteroids (both endogenous and exogenous) cause demargination of neutrophils 5
• Medications that can cause neutrophilia include 3:
  • Corticosteroids
  • Lithium
  • Beta-agonists
  • Epinephrine
• Chronic inflammatory conditions often present with persistent neutrophilia 3
• Smoking and obesity are associated with higher baseline neutrophil counts 3
• Asplenia can lead to elevated neutrophil counts due to decreased clearance 3
• Hematologic disorders and malignancies can cause neutrophilia, particularly when accompanied by symptoms like fever, weight loss, bruising, or fatigue 3

Clinical Significance of Neutrophilia

• The presence of an elevated WBC count (≥14,000 cells/mm³) or a left shift warrants careful assessment for bacterial infection, even without fever 1, 2
• In patients with cirrhosis and ascites, altered white blood cell count is one of the signs of systemic inflammation that may indicate spontaneous bacterial peritonitis 1
• The ratio of neutrophils to lymphocytes (neutrophil-lymphocyte ratio) can reflect the severity of systemic inflammation and stress in critically ill patients 4
• A high percentage of neutrophils (≥82.1%) has been identified as a predictor of long-term mortality in patients with ST-elevated myocardial infarction 6

Diagnostic Approach

• A complete blood cell count with differential should be performed for all patients suspected of having infection within 12-24 hours of symptom onset 1
• Manual differential is preferred to assess bands and other immature forms 1
• In the absence of fever, leukocytosis, left shift, or specific clinical manifestations of a focal infection, additional diagnostic tests may not be indicated 1
• When evaluating neutrophilia, consider the dynamic changes in WBC count and left shift data, as these reflect the progression of bacterial infection from onset to recovery 7

Common Pitfalls

• Overlooking the significance of absolute neutrophil count elevation when total WBC count is only mildly elevated 2
• Treating asymptomatic patients with antibiotics based solely on mildly elevated neutrophil counts 2
• Failing to recognize that time-series data of left shift and WBC count provide more accurate information about bacterial infection than a single measurement 7
• Not considering non-infectious causes of neutrophilia when evaluating a patient with elevated neutrophil count 3